The invention relates to photo lithography technology and, more particularly to a method for forming patterns using a single mask that can easily form line and space patterns using the single mask.
In order to form more fine patterns according to the tendency to produce highly integrated and dense semiconductor devices, photo lithography technology which realizes high resolution has been studied and developed. The resolution (R) of an exposure apparatus is defined as the following Equation 1, wherein k1 is a process constant, λ is an exposure wavelength, and NA is a number of lens apertures in the exposure apparatus.
                    R        =                  k          ⁢                                          ⁢          1          ⁢                      λ            NA                                              Equation        ⁢                                  ⁢        1            
As shown in Equation 1, a number of lens apertures NA in the exposure apparatus must increase and the exposure wavelength λ must decrease to obtain high resolution. In fact, the exposure wavelength used in the exposure apparatus becomes shortened by gradually shifting from I-ray (365 nm) to KrF excimer laser (248 nm) to ArF excimer laser (193 nm) to F2 (157 nm) and the like.
Meanwhile, cell transistors also have been reduced as semiconductor memory devices, for example dynamic random access memory (DRAM) devices, become more highly integrated. With the reduction in size in the cell transistors, the channel length of a gate electrode also decreases, lowering the refresh property, thereby deteriorating the devices. Among the methods for preventing characteristics of a device from deterioration, a method for extending the channel length by forming trenches for recessed channels on a substrate can be mentioned.
FIGS. 1A and 1B are diagrams illustrating a photo mask used in a process of fabricating a recessed gate according to a prior art.
Referring to FIGS. 1A and 1B, the recessed gate according to the prior art uses a mask 10 for recessed channels in a process of etching a substrate to form trenches for recessed channels on a substrate. Subsequently, a mask 20 for gate electrodes to form gate electrodes on the substrate is used. Here, the light blocking regions a and c, and the light transmission regions b and d in the FIGS. 1A and 1B are not described.
Thus, two masks are required in the process of forming a recessed gate according to the prior art. Since the process is performed by using the mask 10 for recessed channels and the mask 20 for gate electrodes respectively in the process of forming the recessed gate according to the prior art, the production cost of the masks and the total fabrication process may increase.